Treatment of vertebral compression fractures commonly employs vertebroplasty and kyphoplasty techniques. Vertebroplasty employs a percutaneous injection of PMMA (polymethylmethacrylate) in a fractured vertebral body via a trocar and cannula.
Kyphoplasty is a modification of percutaneous vertebroplasty. Kyphoplasty involves a preliminary step consisting of the percutaneous placement of an inflatable balloon tamp in the vertebral body. Inflation of the balloon creates a cavity in the bone prior to cement injection. The proponents of percutaneous kyphoplasty have suggested that high pressure balloon-tamp inflation can at least partially restore vertebral body height. In kyphoplasty, some physicians state that PMMA can be injected at higher viscosities and lower pressures into the collapsed vertebra since a cavity exists, when compared to conventional vertebroplasty.
Often in employing Kyphoplasty two straight entries are made into the spine and the inflatable tamp balloons are inflated to form two cavities into which a bone hardening stabilizing cement can be injected. These two points of entry are required because the balloon when entering straight is offset to the left or the right of a midline of the vertebrae as shown in prior art FIG. 1 illustrating one of the inflated balloons.
As a result, to expand the vertebrae to its normal or close to normal original height, the balloon tamp is inflated to lift both sides of the compressed vertebrae. Ideally, the procedure should position the inflatable balloon tamp so it is centered crossing the midline. To accomplish this, the tunneling device must be manipulated in some way to create a path that crosses the midline.
One way is to provide a steerable device; these devices are made of stainless steel and have an internal tensile member that collapses a hinged portion of the outer shaft causing the tip to deflect. This results in a wide windshield wiper motion or sweeping path that does not form a precise tunnel that a balloon tamp can follow to a desirable known position. Steerable devices typically are made as multi-piece structures which are limited in strength running the risk of breakage and leaving portions of a broken device in the patient. These steerable devices all require a physical external manipulation or load to steer the tunnel device.
An alternative is a tunnel device having slots cut in a shaft or cannula to create an effective hinge that collapses under a load or resistance as the device advances in the soft cancellous bone tissue. These slots are cut such that the device bends along a curvature compressing the slots to close along the inside of the radius of curvature, preferably completely collapsing the slot that is to abut the side wall of the adjacent cut out wall. This abutting relationship strengthens the device as it tunnels through the tissue. In this prior art solution the desired curvature can only be achieved by the slots or cuts collapsing under the load created by the patient's tissue resisting the tunnel movement, accordingly, dependent of the patient's anatomy and the force required to close the slots, the device may have an indeterminate tunnel path. In fact, the device may only turn or bend when it upon contact with the hard cortical bone on the opposite side of the vertebrae. The functionality of these devices is dependent on the patient's bone density. These type devices may deflect prematurely, effectively creating a “wind-shield wiper” type cavity in comparatively dense bone, e.g. partially healed fracture, or the device may not deflect at all due to various pathologies that decrease bone density, e.g. osteoporosis.
Ideally, the tunnel device must be capable of achieving a consistent and predictable path that, in the case of vertebrae compression fracture repair, cross the midline to create a balloon tamp path that forms a cavity in the optimal location so the procedure can be accomplished with a single, preferably, small opening.
While the tunnel device of the present invention addresses these issues, it has further applications in any procedure where a single surgical entry requires curvature or bend in a path after entry into a body. This is made possible by the invention as disclosed herein as follows.